HI what is the best music content (genre, style) for performing listening test, in the sense that it does expose possible audio artifacts most reliably ?And additional question, for listening test is it suitable to apply usual DSP effects (gr.equalizer + limiter). WIth these effects the audio sound "better" for me, but not sure if they don't suppres audio artifacts too.

Any listening test is only valid for that listener/material/codec/listening conditions etc. If you regularly listen with DSP effects then what is most valid for you is testing with your settings. This may make some artifacts less obvious, but others more so.

Different genres cause different issues with different codecs, so again test with what you listen to.